1. Field of the Invention
The present invention relates to a fine adjustment mechanism for a scanning tunneling microscope (hereinafter referred to as an STM), and, more particularly, to a three-dimentional fine adjustment mechanism which employs a cylindrical piezoelectric element.
2. Description of the Related Art
Generally, STMs include a combination of a coarse adjustment mechanism and a fine adjustment mechanism, the coarse adjustment mechanism being adapted to hold a sample to be observed and the fine adjustment mechanism having a probe. In such STMs, after the sample has been advanced by the coarse adjustment mechanism to the vicinity of the forward end of the probe, the probe is moved towards the sample by the fine adjustment mechanism while a voltage is being applied between the sample and the probe, until a tunnel current having a predetermined magnitude flows therebetween. Subsequently, the probe is moved along the surface of the sample by the fine adjustment mechanism, so as to detect irregularities on the surface of the sample on an atomic scale utilizing variations in the tunnel current.
The fine adjustment mechanisms for use in these STMs in general employ a cylindrical piezoelectric element, such fine adjustment mechanisms being disclosed, for example, from Page 1688 to 1689 of Rev. Sci. Instrum., Vol. 57 (1986) by G. Binnig and D. P. E. Smith and from Page 145 to 153 of Surface Science , Vol. 181 (1987) by K. Besocke.
In any of these fine adjustment mechanisms, the one end of a cylinder which comprises a piezoelectric element is mechanically fixed to a fine adjustment mounting member, and the other end thereof is provided with a probe. The inner and outer walls of the cylinder are provided with electrodes. When a voltage is applied to these electrodes, mechanical deformity occurs on the piezoelectric element, by means of which the probe is finely adjusted.
The tunnel current that flows between the probe and the sample is picked out through a conductor wire connected to the probe, and is measured by a measuring device.
However, since the tunnel current is at an extremely small level, it is susceptible to variations in the voltage applied to the electrodes of the piezoelectric element and the electrical noises from the outside of the fine adjustment mechanism, making it difficult for the tunnel current to be output at an accurate value.